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United States Patent |
5,058,593
|
Forestieri
,   et al.
|
October 22, 1991
|
Apparatus for processing and displaying ultrasonic data
Abstract
An apparatus and method for displaying ultrasonic data in real time
reflected in a living organism. The apparatus comprises a plurality of
analog-to-digital converters for digitizing reflected Doppler signals
produced by reflecting a reference pulsed acoustic signal, each of the
analog-to-digital converters capable of producing a plurality of digitized
Doppler signals. The apparatus futher comprises a plurality of digital
signal processors, each of the plurality of digital signal processors
coupled to each of the plurality of analog-to-digital converters for
processing digitized Doppler signals received from the analog-to-digital
converters, each of the digital signal processors capable of producing a
plurality of processed digital signals. The apparatus further comprises a
controller coupled to the analog-to-digital converters and the digital
signal processors for controlling the operation of the analog-to-digital
converters and digital signal processors, controlling the receipt of the
processed digital signals, and compressing each of the plurality of
processed digital signals output from the plurality of digital signal
processors into a plurality of signals suitable for display.
Inventors:
|
Forestieri; Steven F. (Santa Clara, CA);
Lin; Sheng T. (Santa Clara, CA);
Lum; John J. (San Francisco, CA);
Rains; William A. (Aptos, CA);
McNerney; Steven A. (Sunnyvale, CA)
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Assignee:
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Diasonics, Inc. (Milpitas, CA)
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Appl. No.:
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584191 |
Filed:
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September 18, 1990 |
Current U.S. Class: |
600/453; 348/163; 600/455 |
Intern'l Class: |
A61B 008/00 |
Field of Search: |
128/660.04,660.05,661.08,661.09,661.07
358/112,166,167
|
References Cited
U.S. Patent Documents
4690150 | Sep., 1987 | Mayo, Jr. | 358/112.
|
4742830 | May., 1988 | Tamano et al. | 128/661.
|
4817619 | Apr., 1989 | Sugiyama et al. | 128/661.
|
4827942 | May., 1989 | Lipschutz | 358/112.
|
4918605 | Apr., 1990 | Shirasaka | 128/660.
|
Primary Examiner: Jaworski; Francis
Assistant Examiner: Manuel; George
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor & Zafman
Claims
What is claimed is:
1. An apparatus for processing Doppler signal data in real time for an
ultrasonic imaging apparatus comprising:
a. a receiver for receiving reflected Doppler signals produced by
reflecting a reference pulsed acoustic signal;
b. a plurality of integrators coupled to the receiver for integrating the
reflected Doppler signals over a first period of time to maximize the
signal-to-noise ratio of the reflected Doppler signals;
c. a plurality of analog-to-digital converters coupled to the integrators
for digitizing the reflected Doppler signals each of the analog-to-digital
converters outputting a plurality of digitized Doppler signals;
d. a plurality of digital signal processors, each of the plurality of
digital signal processors coupled to each of the plurality of
analog-to-digital converters for processing the plurality of digitized
Doppler signals, each of the digital signal processors outputting a
plurality of processed digital signals; and
e. a controller coupled to the receiver, the integrators, the
analog-to-digital converters and the digital signal processors, for
controlling the operation of the integrators, analog-to-digital converters
and digital signal processors, controlling the receipt of the processed
digital signals, and compressing each of the plurality of processed
digital signals output from the plurality of digital signal processors
into a plurality of signals suitable for display.
2. The apparatus of claim 1 wherein the analog-to-digital converters
comprise a first set of analog-to-digital converters for digitizing analog
in-phase reflected signals from the reference pulsed acoustic signal, and
a second set of analog-to-digital converters for digitizing analog
quadrature reflected signals from the reference pulsed acoustic signal.
3. The apparatus of claim 2 wherein the first set of analog-to-digital
converters comprises a first subset of I analog-to-digital converters, the
second set of analog-to-digital converters comprises a first subset of Q
analog-to-digital converters, the first subsets of I and Q
analog-to-digital converters for processing a first set of color sample
volumes in a vector from the reference pulsed acoustic signal, and the
first set of analog-to-digital converters comprises a second subset of I
analog-to-digital converters, and the second set of analog-to-digital
converters comprises a second subset of Q analog-to-digital converters,
the second subsets of I and Q analog-to-digital converters for processing
a second set of color sample volumes in each vector of reflected signals
from the reference pulsed acoustic signal.
4. The apparatus of claim 3 wherein the first set and the second set of
analog-to-digital converters each comprise sixteen analog-to-digital
converters.
5. The apparatus of claim 4 wherein the plurality of digitized Doppler
signals each comprises sixteen bits.
6. The apparatus of claim 4 wherein the plurality of processed Doppler
signals each comprises sixteen bits.
7. The apparatus of claim 4 wherein the plurality of signals suitable for
display each comprises eight bits.
8. An apparatus for processing Doppler signal data in real time for an
ultrasonic imaging apparatus comprising:
a. first and second analog-to-digital (A/D) converters, the first A/D
converters for digitizing analog in-phase reflected (first) signals from a
reference pulsed acoustic signal, and the second A/D converters for
digitizing analog quadrature reflected (second) signals from the reference
pulsed acoustic signal, the first A/D converters having a first set of
first A/D converters, the second A/D converters having a first set of
second A/D converters, the first sets of first and second A/D converters
for processing a first set of color sample volumes in a vector from the
reference pulsed acoustic signal, the first A/D converters further having
a second set of first A/D converters, and the second A/D converters
further having a second set of second A/D converters, the second sets of
first and second A/D converters for processing a second set of color
sample volumes in each vector of reflected signals from the reference
pulsed acoustic signal, the first and second A/D converters outputting a
plurality of digitized Doppler signals;
b. a plurality of digital signal processors, each of the plurality of
digital signal processors coupled to the first and second A/D converters
for processing the plurality of digitized Doppler signals, each of the
digital signal processors outputting a plurality of processed digital
signals; and
c. a controller coupled to the first and second A/D converters and the
digital signal processors for controlling the operation of the first and
second A/D converters and digital signal processors, controlling the
receipt of the processed digital signals, and compressing each of the
plurality of processed digital signals output from the plurality of
digital signal processors into a plurality of signals suitable for
display.
9. The apparatus of claim 8 wherein the first and second A/D converters
each comprise sixteen A/D converters.
10. The apparatus of claim 9 wherein the plurality of digitized Doppler
signals each comprises sixteen bits.
11. The apparatus of claim 9 wherein the plurality of processed Doppler
signals each comprises sixteen bits.
12. The apparatus of claim 9 wherein the plurality of signals suitable for
display each comprises eight bits.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of Doppler ultrasound imaging in
living tissue. Specifically, this invention relates to an apparatus for
processing ultrasonic data suitable for displaying upon a suitable medium,
such as a video display screen, for observation and diagnosis by medical
personnel.
2. Prior Art
Images of living organisms typically utilize methods that pass various
types of radiation through the body of the animal and measure the output
with a suitable detector. For instance, x-ray images are generated by
producing x-rays external to the body, passing the x-radiation through the
body and observing shadows produced on x-ray sensitive film. Ultrasonic
images, in contrast, are formed by producing ultrasonic waves using a
transducer, passing those waves through the body, and measuring the
properties of the scattered echoes from reflections inside the body using
a receptor. Ultrasonic imaging apparatus may be distinguished from other
medical imaging apparatus in the respect that they allow the display of
soft tissues within the body which show various structural details such as
organs and blood flow.
An ultrasonic imaging apparatus utilizes a probe which contains elements
for transmitting acoustic pulses throughout tissue, which probe typically
also contains receiving circuitry which allows reception of the reflected
acoustic pulses. Such probes typically comprise a plurality of elements in
a linear fashion such that each of the elements are fired at time
intervals to focus on specific parts of the body. In other systems,
multiple elements are simulated by means of a moveable mechanical element
within the probe wherein the acoustic pulses are transmitted at various
intervals along an axis. Each reflective pulse from the acoustic pulses
emitted may then be received by a receiving unit located in the probe and
transmitted to circuitry within the ultrasound apparatus for processing
and generation of a display. This display, known as a b-mode image or
two-dimensional image of blood flow velocity, may then be generated by the
apparatus and displayed on a video monitor for diagnosis and examination
by an attending operator or physician.
The basic principle used in applying the Doppler method for ultrasonic
imaging in a pulsed Doppler ultrasound apparatus is described as follows.
When blood flow within a living subject is subjected to ultrasonic waves,
corpuscles are caused to vibrate slightly while moving and reflect those
ultrasonic waves. Because of the corpuscle velocity, the frequency of the
reflected waves changes from that of the transmitted waves because of the
Doppler effect. The frequency shift may be detected and the amount of the
shift may be displayed on a video screen for imaging blood flow in the
living subject. Since the amount of shift of the transmitted waves is in
relation to the blood flow velocity, the amount of blood flow and the
speed of the blood flow may be observed. Noise and other signals (clutter)
which have Doppler shift but don't represent blood movement in the body
are filtered out, so that the image produced only represents blood flow in
motion. In color Doppler imaging the frequency information is then used as
blood flow information for forming a two-dimensional image or profile of
the blood flow velocity.
One such apparatus used in displaying information obtained from ultrasonic
pulses transmitted in the human body is shown in FIG. 1 as imaging system
100. Imaging system 100 generally comprises a probe 101 which is coupled
via line 110 to transmitter/receiver circuitry 102. Transmitter/receiver
circuitry 102 is designed so that the elements in probe 101 will be fired
at specified time intervals, with reflective pulses being detected using
probe 101 at another given time interval. Transmitter/receiver circuitry
102 is coupled to a control unit 109 via bus 120. Control unit 109
controls all circuitry in the imaging system via bus 120. Control unit 109
is further coupled to a keyboard 125 and a mouse, trackball or other
device 126 for movement and control of information shown on video display
130.
Once a pulse is received by the receiver circuitry within
transmitter/receiver 102, such information is transmitted by line 111 to
RF (radio frequency) processor 103 for further processing. RF processor
103 processes the RF information to produce an envelope signal and
in-phase (I) and quadrature (Q) Doppler signals. These signals are further
transmitted via line 114 to a scan converter 105 and to a Doppler
processor 106 via lines 114 and 113 for generation of black and white
ultrasound information on video display 130. Information generated by
Doppler processor 106 via I and Q signals output from RF processor 103 are
transmitted via line 115 to scan converter 105. Scan converter 105 then
integrates information received from RF processor 103 and Doppler
processor 106 and transmits scan line information to video processor 127
via line 116. In addition to information passed to scan converter 105 and
Doppler processor 106, RF processor 103 transmits I and Q signals via line
112 to color flow processor 104. Color flow processor 104 is also
controlled by control unit 109 via bus 120. Color flow processor 104 is
used for detecting Doppler shift and blood flow information in living
tissue, and thus transmits such information via line 117 to a color scan
converter 108. Such color information is used to graphically represent on
video display 130 moving blood flow in a living organism. Color scan
converter 108 is used to interpolate scan line information obtained from
color flow processor 104, and transmit that information on line 118 and
thus to video processor 127 for representation of blood flow in the human
body. Video processor 127 then utilizes information obtained from scan
converter 105 for display of black and white ultrasound information and
color information obtained from color scan converter 108 to generate a
color image showing blood flow overlaid on a black and white image showing
stationary tissue suitable for output on a video display such as 130 via
line 119. Such information may be transmitted in National Television
Standards Committee (NTSC) format and thus be stored on video tape for
later clinical examination by attending medical personnel.
A more detailed representation of a prior art color flow processor 104
shown in FIG. 1 is shown in FIG. 2. 104 shown in FIG. 2 is representative
of a prior art color flow processor. As is shown in FIG. 2, line 112
contains I and Q data from RF processor 103 shown in FIG. 1 to two analog
filters 201. The analog filters 201 are used by the color flow processor
104 to filter out clutter information contained within the Doppler signal.
In other words, analog filters 201 will eliminate signals contained within
the analog Doppler data that indicate no motion. Typically, in a prior art
system such as color flow processor 104 shown in FIG. 2, objects with
little or no motion generate reflected signals below 150 Hz which will be
filtered out by analog filters 201. Analog filters 201 are regulated by
color sample volume (CSV) controller 200, and sample each frequency a
fixed number of times to generate a continuous average for each color
sample volume (CSV). The CSV controller 200 thereby commands analog
filters 201 to sample the Doppler signal at fixed time intervals only.
Coupled to analog filters 201 via lines 210 are matched filter
analog-to-digital (A/D) converters 202 shown in FIG. 2. A prior art
system, such as color flow processor 104, typically comprises a plurality
of A/D converters coupled to filters such as analog filters 201, which
then digitize the analog signal after clutter has been removed. The
matched filter A/D converters 202 are 12 bit resolution converters which
take the signal generated by the analog filters 201 and digitize it to 12
bits of accuracy. This information can then be transmitted to a digital
filter 203 shown in FIG. 2 via lines 211. Digital filter 203 allow
additional removal of clutter information from the Doppler signal which
has been digitized, so that an uncorrupted Doppler signal may be obtained
which is useful for display upon video display 130 in ultrasound imaging
system 100. After the additional clutter has been removed by digital
filter 203, the processed information is transmitted via lines 212 to
parameter estimator 204. Parameter estimator 204 is used for generating
samples of each point along vectors for display on video display 130.
Parameter estimator 204 determines the phase shift and direction of that
shift for each signal in each CSV to generate flow information. This flow
information generally comprises velocity and amplitude information for
reflected Doppler signals. In addition to amplitude and velocity
information parameter estimator 204 generates variance information.
Variance is generally the difference between maximum frequencies and
minimum frequencies for a particular time interval. Parameter estimator
204 is further coupled to interface 205 via bus 214 and output line 213.
Interface 205 controls signals output from parameter estimator 204 into
interface 205 via line 213. Interface 205 then generates appropriate
information over line 117 for transmission to color scan converter 108
shown in FIG. 1.
Essentially, color flow processor 104 shown in FIG. 2 requires extensive
analog filtering via analog filters 201 prior to digitization of the input
Doppler signals for color flow parameter extraction. This is because there
is too much clutter in the signal prior to digitizing to resolve a signal
with only 12 bits of information. Since various analog processing must be
performed prior to digitization, flexibility is lost since information
which is filtered out might otherwise be available by adjusting filter
parameters. Therefore, an apparatus is required for determining Doppler
flow data which allows convenient adjustment of filters for ultrasonic
imaging. In addition, since the prior art limited digitization of flow
data from color scan vectors to 12 bits, an increase in resolution of such
digitized signals would be useful.
SUMMARY AND OBJECTS OF THE INVENTION
One object of the invention is to provide real-time color flow processing
and digitization which allows adjustment of input filters for clutter and
stationary object removal.
This and other objects are provided for by an apparatus for processing a
Doppler signal data in real time which comprises a plurality of
analog-to-digital converters for digitizing reflected Doppler signals
produced by reflecting a reference pulsed acoustic signal. Each of the
analog-to-digital converters is capable of producing a plurality of
digitized Doppler signals. The apparatus further comprises a plurality of
digital signal processors, each of the plurality of digital signal
processors coupled to each of the plurality of analog-to-digital
converters for processing digitized Doppler signals received from the
analog-to-digital converters. These digital signal processors are capable
of producing a plurality of processed digital signals. The apparatus
further comprises a controller coupled to the analog-to-digital converters
and the digital signal processors for controlling the sampling rates and
operation of the analog-to-digital converters and digital signal
processors. The controller regulates the receipt of the processed digital
signals, and the compression of each of the plurality of processed digital
signals output from the plurality of digital signal processors into a
plurality of signals suitable for display.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not limitation
in the Figures of the accompanying drawings in which like references
indicates similar elements and in which:
FIG. 1 shows a prior art ultrasonic imaging system.
FIG. 2 shows a detailed representation of a prior art color flow processor
in an ultrasonic imaging system.
FIGS. 3A and 3B show a detailed representation of a color flow processor
used in the preferred embodiment.
FIG. 4 shows a representation of vectors and color sample volumes used to
generate ultrasonic images for display in the preferred embodiment.
DETAILED DESCRIPTION
The present invention covers an apparatus for acquiring ultrasonic imaging
data, and displaying that data on a suitable display, such as a video
display screen. In the following description, numerous specific details
are set forth such as specific hardware components, bit lengths, etc., in
order to provide a thorough understanding of the present invention. It
will be obvious, however, to one skilled in the art that these specific
details may not be required to practice the instant invention. In other
instances, well-known components of ultrasonic imaging apparatus have not
been described in detail to not unnecessarily obscure the present
invention.
FIGS. 3A and 3B illustrate a color flow processor known as the color
Doppler imaging (CDI) module 300 which may be used in place of the prior
art color flow module 104 of the system shown in FIGS. 1 and 2. CDI module
300 basically comprises three distinct components: a color data
acquisition (CDA) board 302; a color Doppler processor (CDP) board 303;
and a color Doppler controller (CDC) board 301. CDA board 302, and CDP
board 303 are both linked via bus 340 to CDC board 301 for the control of
sampling, processing, and timing of signals internal in CDI module 300.
CDC board 301 is linked to the remainder of ultrasonic imaging system 100
via bus 120. CDC board 301 synchronizes each transmit/receive cycle of the
acoustic pulses for Doppler processing. In other words, for each given
acoustic pulse of the reference wave, the apparatus will wait a given
period of time before the receiver circuitry is enabled. CDC board 301
also synchronizes each sampling of the Doppler data by CDA 302 and the
corresponding DSP board 303 for signal processing. In addition, as shown
in FIG. 3B, CDC board 301 comprises a color scan converter (CSC) interface
304 for converting processed information to a form suitable for display.
The next major element in CDI module 300 is the color data acquisition
(CDA) board shown as 302 on FIGS. 3A and 3B. CDA board 302 comprises two
major components: an analog in-phase (I) section 310; and an analog
quadrature (Q) section 311. The analog in-phase section handles I data
received from the radio frequency processor 103 via line 112. Analog
quadrature section 311 handles Q data received from the processor 103 via
line 112. Q section 311 is identical to I section 310 so only I section
310 is discussed here. In order to understand the architecture of each
portion of CDA board 302, a discussion of vectors and color sample volumes
(CSV's) in an ultrasonic imaging apparatus is required.
Referring to FIG. 4, a general representation of vectors and color sample
volumes (CSV's) shown as 400. 400 may be loosely viewed as a
representation of a two-dimensional area being scanned in a living
organism and displayed on video display 130 of FIG. 1. Each column in 400
such as 410 is known as a vector and generally corresponds with a
transducer element on a linear array type probe 101 of imaging apparatus
100. Alternatively, each vector may correspond with an element position
for a motorized probe 101 in an alternative embodiment. Each element in a
linear array probe 101 is used in both active and passive mode for
transmitting and receiving acoustic pulses during transmit/receive (t/r)
cycles of ultrasonic imaging apparatus 100. Also shown in 400 are rows 420
which are known as color sample volumes (CSV's). Therefore, for each
vector such as 410 (element in a linear array probe or element position in
a mechanical probe), there are a plurality of CSV's 420. Each CSV
corresponds with a given depth in the scan area. So CSV 413 in vector 410
will be at a shallower depth than 415 of vector 410. In the preferred
embodiment, each CSV may range between 0.5 millimeters and 1 centimeter in
length. The total number of CSV's in each vector ranges between 1 and 128.
Returning to FIG. 3A, I section 310 comprises 8 matched filters 321
electrically coupled to an equal number of gain selects 320 which are
coupled to input line 112 containing the I analog signal from RFP 103 of
apparatus 100. Each matched filter such as 325 allows integration of the I
signal over a period of time in order to optimize the signal-to-noise
ratio of the signal passed to analog-to-digital (A/D) converters 323. Each
matched filter integrates the signal over a period equal to the CSV or the
amount of time when one CSV is received by the transducer to the next CSV.
The amount of time matched filters 321 integrate is dependent upon the
pulse repitition frequency (PRF--the frequency of the acoustic reference
pulse from which a phase-shift and thus blood flow velocity may be
determined). Each matched filter gain select such as 324 shown in FIG. 3A,
has four possible settings depending on the length of each CSV and the
time between each sampled CSV. Each matched filter gain is selectable via
software with increases in gain being required for smaller CSV's. Matched
filters 320 are further connected to a buffer area shown in FIG. 3A as
buffers 322. Each buffer is then connected to a pair of corresponding A/D
converters. For example, as shown in FIG. 3A buffer 326 is electrically
coupled to matched filter 325 and matched filter gain select 324 is
further coupled to A/D converters 327 and 328. These A/D converters will
now be discussed.
Analog Q section 311 and analog I section 310 each comprise 16 A/D
converters. The A/D converters are shown as 323 for I section 310. A/D
converters 323 shown in analog I section 310 are coupled to the matched
filter buffers 322. Each buffer such as 326 shown in FIG. 3A, is coupled
to two A/D converters. For instance, as shown in FIG. 3A, buffer 326 is
electrically coupled to the first A/D converter 327 and the ninth A/D
converter 328. This allows digitizing of a first set of eight CSV's by the
first set of eight A/D converters in block 323 (A/D converters 327 to
377), and the next set of eight CSV's to be processed by the second set of
eight A/D converters shown in block 323 (A/D converters 328 to 329). The
same matched filters, however, are used for every eight CSV's. Therefore,
as each CSV in a vector is processed, the first matched filter 325 and the
first A/D converter 327 will filter and digitize the signal. The second
CSV in the vector will be processed by the second matched filter 371 and
second A/D converter 373. This continues until the ninth CSV in the
vector. When the ninth CSV is received by the receiver circuitry in probe
101, the first matched filter 325 will process the signal, however, the
ninth A/D converter 328 will digitize the signal. The sampling of the
second set of CSV's will continue until the eighth matched filter 375
obtains the last in the second set of CSV's. That signal is digitized by
the sixteenth A/D converter 329. On the next sampling cycle of the CSV's,
the process starts over with the first matched filter 325 receiving the
first CSV and the first A/D converter 327 digitizing the signal.
For instance, with reference to FIG. 4, the first eight CSV's 411 in vector
410 will be digitized by A/D converters 327 through 377. CSV 413 in vector
410 will be processed by gain select 324, matched filter 325, buffer 326
and digitized by A/D converter 327. The next CSV 415 in vector 410 will be
processed by gain select 370, matched filter 371, buffer 372 and digitized
by A/D converter 373. The eighth CSV 417 in vector 410 will be processed
by gain select 374, matched filter 375, buffer 376 and be digitized by A/D
converter 377. The next CSV 418 in vector 410 will be processed by gain
select 324, matched filter 325 and buffer 326, but will be digitized by
the ninth A/D converter 328. As mentioned previously, this will continue
until the second set of eight CSV's 412 have been processed wherein CSV
419 will be processed by 374, 375, and 376, and will be digitized by the
sixteenth A/D converter 329 shown in FIG. 3A. The next eight CSV's in
vector 410 will then be processed by the first eight A/D converters, and
so on, until the last CSV 416 in vector 410 has been processed.
Each A/D converter in analog I section 310 generates serial data output on
lines 330 shown in FIGS. 3A and 3B. The digitized signals from the A/D
converters of analog Q section 311 of CDA board 302 are also output in a
serial fashion on lines 331 of FIGS. 3A and 3B. Lines 330 and 331 are
input to a delay multiplexing circuit shown generally as 350 in FIG. 3B
and output onto lines 332. Each multiplexing circuit of 350, for instance
351, will delay by sixteen bits the data received from lines 331.
Therefore, data on lines 332 will first be received from lines 330
serially for 16 bits of data. Then, data will be received from lines 331
(which have been delayed by 16 bits) and continue on lines 332. Therefore,
each digital signal processor in section 360 of DSP board 303 will receive
the data over lines 332 in a serial synchronized fashion with the sixteen
bits of I data from lines 330 preceding the sixteen bits of Q data
received from lines 331. The most significant bit of each of the I and Q
data will be transmitted first. Circuit 350 therefore transforms each of
the I and Q digitized data into a 32 bit synchronous bit stream. This is
accomplished through the use of a PAL (Programmed Array Logic) in the
preferred embodiment, but circuit 351 may be a shift register or other
similar circuitry coupled to lines 331 in alternative embodiments.
All data is transmitted from A/D converters 323 in a serial synchronized
fashion and is clocked at a rate of 4.8 MHz by CDC board 301. Each of the
lines 332 from circuit 350 is received by digital signal processors
(DSP's) 360 shown in FIG. 3B. As shown in FIG. 3B, CDP board 303 comprises
16 digital signal processors 360 along with their corresponding memories
365. Each DSP used in CDP board 303 of the preferred embodiment, such as
361 in FIGS. 3A and 3B, is an AT & T DSP 32C 32-bit floating point digital
signal processing chip manufactured by American Telephone and Telegraph.
Each digital signal processing chip such as 361 allows digital filtering
of the signals received over lines 332 received from CDA board 302 shown
in FIG. 3A. Each DSP performs operations on each 32 bit word (combined I
and Q data) that is received over lines 332.
First, for each 16 bit word for the I and Q data respectively, the values
are tested to determine whether they have reached a saturation or overflow
condition. If the value has reached an overflow condition, then an
overflow counter for the particular I or Q value is incremented. Then,
each of the I and Q values, respectively, are converted from their fixed
point representation generated by the 16 bit A/D converters 323 to a
floating point representation may be used within the DSP's for filtering
and computation of various information. Calculations are then performed on
the filtered data to extract estimates of three parameters from the
Doppler shift information. These are I(n), the intensity of the Doppler
signal, F(n), the mean frequency shift of the Doppler signal, and V(n),
the variance of the frequency shift of the Doppler signal.
After computation of the three flow parameters, the values of I(n), F(n)
and V(n) are converted to a fixed point representation, and combined into
a 16 bit word for output to the CSC interface 304, which is a part of CDC
board 301. From there, data is transmitted to the color scan converter 108
via line 117. In the preferred embodiment, the four most significant bits
of the word transmitted on line 391 to the CSC interface 304 contain I(n)
(intensity), the next six bits contain V(n) (variance) and the last six
bits contain F(n) (frequency or velocity). These are transmitted by CSC
interface 304 to the color scan converter 108 in an eight bit parallel
fashion over line 117 for interpolation between vectors and CSV's by color
scan converter 108. The result may then be displayed on video display 130.
Using the architecture of the preferred embodiment, it can be appreciated
that no clutter or fixed target removal must be done prior to digitization
for processing and display by flow processor 300, as in the prior art
color flow processor 200 described with reference to FIG. 2. Since the
filtering and clutter removal has all been accomplished at the level of
the DSP's 360, shown in FIG. 3B, convenient manipulation of control and
filtering parameters of the various equations for generating the
intensity, variance and frequency information may be accomplished, varying
the sensitivity of the apparatus as well as adding flexibility.
In the foregoing specification, the invention is described with reference
to specific embodiments thereof. It will, however, be evident that various
modifications and changes may be made thereto without departing from the
broad scale or spirit of the invention as set forth in the appended
claims. The specification and drawings are, accordingly, regarded in an
illustrative rather than a restrictive sense.
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